1. Field of the Invention
The present invention relates to electronic visual displays for displaying an image. More particularly, the present invention pertains to a light valve structure and fabrication method ID for use in a projection-type visual display.
2. Description of the Related Art
There are various types of visual electronic displays for displaying or imaging video information. For example, cathode ray tubes have long been employed in televisions and computer monitors wherein electron guns generate electrons which illuminate a target screen in response to an electronic signal. The electronic signal is typically derived from a transmitted video signal received by a receiver connected to the electron guns. The problem with such known systems is that they require relatively high voltages to operate the electron gun and to accelerate the emitted electrons.
Another type of display is a projection system which employs light valves to convert video signals into a viewable image which is then projected on a screen. One type of light valve technology is a grating light valvetrade (GLV) which is a micromechanical phase grating. By providing controlled diffraction of incident light, a GLV device will produce bright or dark pixels in a display system. With pulse width modulation, a GLV device will produce precise gray scale or color variations. Built using microelectromechanical systems (MEMS) technology, a GLV device can be made both small and inexpensively. A variety of display systems can be built using GLV technology, each benefiting from the high contrast ratio, fill ration and brightness. In addition, GLV technology can provide high resolution, low power consumption and digital gray-scale and color reproduction. A drawback of GLV technology is that it is complex to construct a matrix or two-dimensional array of pixels. If a one-dimensional array is constructed, mechanical scanning can be used to simulate a two-dimensional array.
Liquid crystal on silicon (LCOS) has also been used in projection display applications. This technology offers an inexpensive way of projecting an image on a screen. LCOS systems require polarized light for operation which results in a problem of color management in the polarization modulating panels. In LCOS panels, the polarization of incoming light results in a 50% decrease of the available light. Although polarization recovery systems can be used to improve the efficiency of light usage, such systems will only increases the efficiency to approximately 80%.
Still other types of light valves or light modulators comprise a deformable layer of material (commonly referred to as a gel layer), which is disposed over an array of electrodes. One such system is disclosed in U.S. Pat. No. 3,882,271 (Glenn). Such modulators include a metal reflective layer disposed on the surface of the gel which serves both as an electrode and as a light-reflecting medium.
The present invention is directed to a light valve or pixel structure for use in an electronic visual display. The structure includes a semiconductor substrate having an upper surface with reflective conductors formed thereon. The conductors function as electrodes and are arranged into groups, with each group including an actuation electrode and a grounding electrode. A layer of transparent material is disposed on the electrodes. The transparent material is deformable in response to an electric field generated by the electrodes, which occurs when a voltage is applied to the electrodes. When light is incident on the transparent material, the light transmits through the material, reflects off of the electrodes, and again traverses the material layer. When the electrodes are activated, deformation in the material layer functions as a wavelength diffraction grating which diffracts the reflected light. The light can then be directed to a lens for focusing on a projection screen for displaying an image.
In another preferred embodiment, the layer of deformable material is formed on a transparent electrode supported by a transparent substrate. The deformable material is spatially disposed in opposing relation to a reflecting electrode formed on a semiconductor substrate. When a voltage is applied to the reflecting electrode, an electric field is formed between the reflecting electrode and the transparent electrode which causes deformations in the deformable material layer. As a result, incident light is diffracted by the deformations in the material.
In yet another preferred embodiment, a transparent electrode is formed on a second substrate positioned at a distance from the deformable transparent material. When a voltage drop is applied across the reflecting electrode and the transparent electrode, an electric field is formed between the reflecting electrode and the transparent electrode which causes deformations in the deformable material layer. As a result, incident light is diffracted by the deformations in the material.
The present invention is also directed to a method of forming a light valve device for diffracting and reflecting incident light. The method involves the positioning of a substrate formed of semiconductor material and forming a reflective electrode on a surface of the substrate. The reflective electrode is capable of receiving voltages for generating an electric field. A transparent substrate having a transparent electrode formed thereon is disposed at a distance above the reflective electrode. A layer of transparent dielectric material is then disposed on either of the transparent or reflective electrodes. The transparent dielectric material is capable of being deformed in response to the electric field so that when incident light is received by said substrate surface, the light will be diffracted by deformities in the layer and reflected by the electrode away from the surface.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.